US 20050117336 A1
The invention relates to an illuminating device comprising a light source (1, 9), disposed along a line, for illuminating a line surface (3), and at least one linear optical element (2, 10). In order to compensate for the vignetting produced by the optical element (2, 10), a diaphragm (6) is provided that produces a numerical aperture that is variable in the direction of the line.
1. Device for illuminating a line surface (3) having a light source (1, 9) designed linearly or being linearly arranged and having at least one linearly formed optical element (2, 10), wherein in the region of said optical elements (2, 10) of said light source (1, 9) said device comprises at least one diaphragm (6) which effects a variable numerical aperture in the direction of the line.
2. Device according to
3. Device according to
4. Device according to
5. Device according to
6. Device according to
The present invention relates to a device for illuminating a line surface according to the preamble of claim 1.
Such illuminating devices are used in reading apparatuses, that is in scanners or optical identification devices, for example in inspection stations for the industrial manufacture of products or identification devices for reading bank notes, bar codes etc.
These illuminating devices all comprise a light source disposed along a line, which light source can be a fiber-optical light source, a tube lamp or a row of electro-optical elements or LED's. In order to guide the emitted light towards a line surface to be illuminated, spherical or aspherical rod-shaped lenses or self-focussing lens arrays are used. Also known are illumination devices having parabolic or elliptically formed reflectors for guiding the light onto the line surface to be illuminated.
The use of rod-shaped lenses made of glass or synthetic material as well as the use of reflectors results in image errors, especially aperture errors and astigmatism which, in turn, influences the intensity distribution on the illuminated line surface. In particular the intensity in the region of the edges decreases. This decrease in brightness is particularly noticeable/pronounced/evident at the ends of lines.
It is therefore the aim of the present invention to correct the decrease in brightness at the ends of lines and to obtain a homogenous distribution of intensity along the entire illuminated line.
This aim is solved by the present invention in that a device for illuminating a line is provided which has the features of claim 1. In particular, this device comprises at least one element acting as a diaphragm which effects a variable numerical aperture in the direction of the line. This variable numerical aperture is designed in such a manner that the vignetting produced by an imaging lens and the natural decrease in light intensity associated therewith according to E(w)* cos4(w) is corrected. It is to be understood that the expert may vary the geometrical shape of the diaphragm as required. With respect to the longitudinal middle axis of the line surface this variation can be either symmetrical or asymmetrical. A suitable mechanical arrangement allows to slidably insert the diaphragms on both sides symmetrically or asymmetrically into the beam path. It is to be understood that just one diaphragm may be inserted from the side. Non-transmissive, transmissive or latticed materials may be used as diaphragm. For this it is possible to also use transmissive phase objects or structured filters etc. It is further possible to use two diaphragms having different spectral transmission values, in order to obtain a specific color combination. These diaphragms have been shown to be especially advantageous when using opto-electrical or fiber-optical line illuminators.
The invention shall be more closely described in the following exemplary embodiment and with the aid of the Figures.
The illumination device shown in
A flat fiber optic 9 arranged in a casing 8 is used as a light source in the illuminating device shown in
The schematically shown arrangement of the illuminating device according to the invention in
In the device shown in
The embodiment as shown in
Other arrangements of the diaphragm 14 are within the scope of the expert. The expert will select the shape of the edge of the diaphragm 14 according to the desired numerical aperture.
The advantages of the present illumination device are immediately evident to the expert and are to be seen in particular in the simplicity of the technical solution. With the present arrangement it is possible to evenly design the operating parameters (and the lifetime) of the LED's used, because these do not have to be operated at differing capacities (luminosity). The inhomogeneousness of the luminosity distribution in a line surface caused by LED's which are differently spaced from each other can be avoided by the use of an arrangement according to the present invention.